1. Field of the Invention
The present invention relates to a dynamic viscoelasticity measuring apparatus and more particularly to an enclosed type dynamic viscoelasticity measuring apparatus of torsional vibration type in which a pair of dices disposed in opposed relationship define a specimen chamber and one dice is imparted with rotary vibration of a predetermined amplitude so that a torque transmitted to the other dice is detected.
2. Description of the Prior Art
A dynamic viscoelasticity measuring apparatus of torsional vibration type (referred to as dynamic viscoelasticity measuring apparatus hereinafter) is an apparatus for detecting a change of viscoelastic properties (referred to as cure rate) while a viscoelastic material is being cured. Such an apparatus is used to determine whether or not a viscoelastic material such as unvulcanized rubber or uncured thermoset (referred to as specimen, hereinafter) has predetermined physical properties after vulcanization or curing. Such apparatus as described above is disclosed in, for instance, U.S. Pat. No. 3,488,992 or Japanese Patent Application Laying-open No. 53-144,794. Such apparatus measures a change of cure rate of specimen with time while heating it, thereby automatically recording a so-called curing curve. Important physical properties of the specimen can be obtained by analyzing the thus obtained curing curve. It can be also determined that a number of specimens have the same physical properties by confirming that substantially the same curing curve is obtained for a number of specimens.
FIG. 1A shows, for instance, a viscoelasticity measuring apparatus as disclosed in Japanese Patent Application Laying-open No. 53-144,794. Reference numeral 1 denotes a detection dice disposed on the detection side and reference numeral 2 is a driving dice disposed in opposed relationship with the detection dice 1. The detection dice 1 is securely mounted on a torque detection shaft 3, while the driving dice 2 is securely mounted on a vibration shaft 4.
The vibration shaft 4 is pivotably mounted on a lower base 5 and has a lower end connected through crank arms 6 and an eccentric shaft 7 to a motor 8 so that periodic vibrations may be imparted to the vibration dice 2.
The detection shaft 3 is pivotably fixed to an upper base 9 and a torque sensing load cell 11 is attached to one end of a torque arm 10, the other end of which is securely fitted to the upper end of the detection shaft 3. An air cylinder 12 is provided so as to move the upper base 9 vertically.
Reference numerals 13 and 14 are heating plates mounted through insulating members 15 and 16 to the upper and lower bases 9 and 5, respectively. Reference numerals 17 and 18 are stationary dices fixed to the heat plates 13 and 14, respectively. A ring-shaped packing 19 is interposed between the stationary dice 17 and the detection dice 1, while a ring-shaped packing 20 is interposed between the stationary dice 18 and the driving dice 2, so that a specimen is prevented from leaking from a specimen chamber 21 which is tightly defined between the detection and driving dices 1 and 2.
Reference numeral 22 is a groove formed around the periphery of the specimen chamber 21 so that the overflow flash of the specimen charged into the specimen chamber 21 can be received in this groove 22. Reference numerals 23A, 23B, 24 and 25 are heaters disposed adjacent to the dices 1 and 2.
In the viscoelasticity measuring apparatus of the type described, the upper base 9 is lifted by the air cylinder 12 so that the detection and driving dices 1 and 2 are moved away from each other. A specimen is placed upon the driving dice 2 and then the upper base 9 is lowered so that the rubber specimen is enclosed in the specimen chamber 21 which is tightly defined between the dices 1 and 17 and the dices 2 and 18. Thereafter, while the specimen is maintained at a predetermined temperature by the heaters 23A, 23B, 24 and 25, the driving dice 2 is reciprocated by the driving mechanism. The motion of the driving dice 2 is transmitted to the specimen and a torque which is transmitted from the specimen through the detection dice 1 and the torque arm 10 is detected by the load cell 11. A torque transmitted is increased in response to the increase of cure rate with time. A change of the torque can be detected by the load cell 11.
However, the viscoelasticity measuring apparatus of the prior art has a rotary motion mechanism of the type in which the vibration shaft 4 is vibrated by the motor 8 through the eccentric shaft 7 and the crank arm 6 connected thereto in order to realize the periodical vibration of the driving dice 2. Accordingly, a periodical vibration with a predetermined period and a predetermined amplitude can be imparted to the driving dice 2, but the apparatus has a disadvantage in that a reciprocal vibration does not have a sinusoidal waveform.
Asymmetry of such a reciprocal vibration will be described with reference to FIG. 1B. Reference numeral 26 denotes the junction between the crank arm 6 and the eccentric shaft 7 which is rotated by the motor 8 and reference numeral 27 denotes the junction between the crank arms 6A and 6B. A phase error and the asymmetry of the operation of this mechanism with respect to a sinusoidal waveform can be simply explained in terms of the positions 26A and 26B of the junctions 26. That is, the positions 6A and 6B assumed by the connection on the drive shaft side correspond to the midpoint of the forward stroke and the backward stroke of the arm 4, respectively. If the arm 4 is driven in the sinusoidal waveform, the positions 6A and 6B of the connection on the drive shaft side would be symmetrical with respect to the drive shaft 1, so that their phase difference should be 180.degree..
However, as can be clearly seen in the figure, the aforesaid positional relation does not exist, and a phase error .alpha. is produced. The phase error .alpha. is equal to the oscillation amplitude angle (indicated by .beta. in the figure). To reduce the value of .beta. with respect to the same angle .theta., the lengh of the arm 6B has only to be increased as compared with those of the radius of rotation and the length of the arm 6A. However, since there is a spatial restriction to the actual system, it is usual practice to design the arms in a manner that the length of the arm 6A is substantially equal to the length of the arm 6B. As a result, the angle .beta. is substantially equal to the angle .theta.. Consequently, in conversion mechanisms of the prior art, the drive waveform thus obtained can be said to be asymmetrical in that the phase error at the midpoint of its oscillation is substantially the same as the amplitude angle of the drive.
However, in the measuring apparatus of the type in which a torsional vibration with a predetermined amplitude angle is imparted to a viscoelastic material to obtain dynamic viscoelastic properties such as storage modulus, loss modulus, phase angle and so on based upon an exact relationship between the resulting torque waveform and the vibration waveform, data analysis is made on the assumption that the vibration waveform is exactly sinusoidal. In this case, it is especially preferable that the sinusoidal waveform is symmetrical without any distortion. As described above, however, the apparatus of the prior art cannot produce such an ideal waveform.
In the apparatus in which a viscoelastic specimen is used, the symmetry of distorted waveforms is very important. The reason is as follows. When a vibration of a periodical sinusoidal waveform with a predetermined period and a predetermined amplitude such as torsional angle strain is being imparted to such a viscoelastic material, the resulting vibration stress (for instance, torque) is represented as shown in FIG. 2.
In FIG. 2, .vertline.M*.vertline. is an amplitude of torque. M.sub.A is a magnitude of torque when an angular waveform S.sub.A assumes a maximum (to be referred to as "elastic component of torque"). M.sub.B is a magnitude of torque when an angular waveform S.sub.A assumes zero in phase (to be referred to as "viscosity component of torque" or "loss torque"). .delta. is a difference in phase between the torque waveform S.sub.B and the angular waveform S.sub.A and is referred to as "phase angle or loss angle".
The above-described terms .vertline.M*.vertline., M.sub.A, M.sub.B and .delta. satisfy the following equations (1) and (2). In order that these equations (1) and (2) are satisfied, the angular waveform S.sub.A must be an exactly sinusoidal waveform without any distortion. ##EQU1##
The loss torque M.sub.B is a torque produced when the angular waveform S.sub.B passes the midpoint, so that when the midpoint does not coincide with the phase 0.degree., 180.degree. or 360.degree., the loss torque M.sub.B contains an error corresponding to such a difference of phase.
Especially, when vulcanization of rubber is made the loss angle .delta. after vulcanization is extremely small. For instance, the loss torque M.sub.B is about 1/10-1/1000 of the torque amplitude .vertline.M*.vertline.. Accordingly, the error of the loss torque M.sub.B cannot be relatively decreased, unless the error due to the asymmetry of the waveform is extremely small at the midpoint of the angular waveform S.sub.A.
This is the reason why an exactly sinusoidal waveform must used as the angular waveform in a viscoelasticity measuring apparatus, especially for rubber material, when tan .delta. or M.sub.B is obtained.
Furthermore, in a viscoelasticity measuring apparatus of the prior art, a time required for measuring one specimen is of the order of a few minutes at most in most cases. Therefore, if a loading of a specimen and a removal of a tested specimen are carried out manually, there is a problem in rationalizing process control.
In order to solve the above and other problems, there has been proposed to use a robot to load a specimen in an apparatus and to remove a tested specimen therefrom. In such a case, it is required that the robot accomplishes a step of receiving a specimen at a predetermined reception position and transporting it to a dice at a measurement position and a step of removing a tested specimen from the measurement position. In such a case, if the robot advances to and retreats from the measurement position sequentially every time that a specimen is loaded or removed, a relatively long time is required, so that it becomes useless to use the robot. Furthermore, in a viscoelasticity measuring apparatus of the prior art, a tested specimen is attached to the upper or lower dice at random, so that it is difficult to use the robot.